This invention relates to a battery charger.
A conventional battery charger includes a temperature sensor for detecting the temperature of a battery; a charging completion sensor for detecting whether a battery has been fully charged; and a means for displaying whether a battery is being charged or whether charging of a battery has been completed. With the conventional battery charger, when the temperature sensor detects that the temperature of the battery is lower than a predetermined value, the charging of the battery is carried out. Charging of the battery is suspended temporarily when the temperature sensor detects that the temperature of the battery is higher than the predetermined value. The charging of the battery is stopped when the charging completion sensor detects that the battery has been fully charged.
With respect to a secondary battery such as a nickel-hydrogen battery, the following facts have been well known in the art: A secondary battery is raised in temperature when charged. When the ambient temperature is high, then the temperature of the battery is greatly increased, which may shorten the service life of the battery. Hence, in charging such a battery, a temperature sensor is provided to detect the temperature of the battery. That is, when the temperature of the battery is abnormally raised, the temperature sensor detects this abnormal temperature rise, so that the charging of the battery is suspended. When, thereafter, the temperature of the battery is lowered to the predetermined value, the charging of the battery is restarted again. The charging of the battery, and the suspending of the charging of the battery are repeatedly carried out until the battery is fully charged. When the charging completion sensor detects that the battery has been fully charged up, the charging of the battery is finished.
As was described above, in the case where the ambient temperature is high, the battery is charged intermittently, and therefore it takes a long time of period to charge the battery completely. On the other hand, during charging, the display means displays the fact that the battery is in being charged. Hence, when compared with a standard charging time determined from a charging current and a battery capacity, the actual charging time is considerably long. This may lead the user to a misunderstanding that the charging completion sensor does not work and the battery charger runs continuously.